Heavy climbers beware! Page 1 of 8

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1 Heavy climbers beware! Page 1 of 8 To my fellow 176 pound (80 kg) and up climbers, please continue reading! You can consider yourself a heavy climber for the purposes of this article. To those of you in the Katie Brown lower weight classes, no offense, but in these days of information overload you might want to skip over this one. You ll be hard pressed to be carrying enough gear to consider yourself a heavy climber, breaking the 176 pound mark. We ve all seen those UIAA test results tagged somewhere on all climbing ropes sitting in the stores which include impact force and number of falls held. Some of us pay a lot of attention to them, others don t. Whichever category you fall into, you need to be aware that these test results are based on a standard test weight of 176 pounds (80 kg) being dropped on the rope until it breaks. If you re less than this weight, you re in the clear. If you re over this weight, at one time or another you ve probably been somewhat concerned about your safety and asked yourself something like, Since I m pounds over that test weight, how do those impact force and number of falls really relate to me? Chances are that you never really found an answer to your question, let go of the thought, and safely went on about your climbing adventures without incident. The truth of the matter is that today s climbing ropes and gear bless us with very safe performance as we engage in our potentially dangerous past time. Today s climbing ropes rarely ever fail, but when they do they re cut versus pulled to failure from excessive loads. Most of your other climbing equipment will fail or pull out of the rock from high loads before your rope will ever break. However, we must never forget the ropes and our gear are NOT indestructible and high impact forces are our enemy! Here s some background why.

2 Heavy climbers beware! Page 2 of 8 What are 80 kg and 12 kn all about? 80 kg (176 pounds) is this nice round magical number the UIAA selected to represent an average climber for the falling body in the required drop test. In the standard drop test the weight is connected to a rigid anchor by about a 4 meter length of rope. The belay end of the rope is anchored a short distance below a smooth edged hole in a steel plate (simulating a fat carabiner ). Then the climber s end of the rope is threaded through this hole (top anchor) and tied to the test weight. Before the drop test the length of the rope is adjusted so that the weight hangs exactly 2.5 meters below this top anchor. (see figure 1) To perform the drop test the weight is raised 2.3 meters above this top anchor and released for a 4.8 meter fall. Using the details of the drop test configuration this fall factor (length of fall divided by length of rope out) measures in at a hefty 1.7. As many of you already know, the maximum fall factor you could achieve in a lead-climbing fall is 2.0. To do this you d have to fall directly onto and past your belay (see figure 2). Figure 2 To go along with this 80 kg test mass, the UIAA also adopted an old US Military specification (1) of 2700 lbf (pounds force), aka 12 kn. This number is what our government once accepted as the maximum allowable force that a paratrooper could withstand when his parachute deployed and jerked his free falling body to a much slower rate of descent. So, simply translate all that to a climber taking a severe fall and you get the picture. Luckily, all of today s climbing ropes are well below that safety limit when tested with 80 kg. So, what happens when Joe Climber is more than 80 kg and takes a hard fall? Could Joe be subjecting himself and his gear to unsafe loads? How hard of a fall does Joe have to take before he comes close to unsafe loads? Serious questions indeed, but they re not addressed by the UIAA testing requirements. Figure 1 Figure 1

3 Heavy climbers beware! Page 3 of 8 Over the years both PMI employees and customers had been asking these basic types of questions. Since nobody seemed to have a concrete answer, we said we d find out. Modify the test To try and answer those questions we had to make some changes to the standard UIAA drop test. All the data from the 39 individual drop tests conducted for this project are provided in the table and graph found at the end of this article. The first part was to simply increase the weight. Speaking in good-old American units for a bit, we started with the standard 176 pounds and went on to test 200, 225, 250, 276, and 301 pounds (respective masses in kg are 80, 91, 102, 114, 125, and 137). Each weight was dropped in the standard 1.7 fall factor setup and the impact forces were measured. Each drop test was performed using a new identical and unused piece of rope. To no one s surprise, as we increased the weight the forces increased. The second part of the testing was to reduce the length of the drop for each of the heavier masses until the impact force was comparable to the standard UIAA single rope drop test using 80 kg. Sound confusing? Consider this example: In the standard test 80 kg was dropped a distance of 4.8 meters and gave an impact force = 8.3 kn. When we increased to 91 kg and dropped it the same distance, the impact force increased to 9.1 kn (or 10%). Then we did more drop tests in which we continuously reduced the fall factor by 0.1 for each consecutive drop until we measured an impact force close to the standard test. With the 91 kg test mass, this occurred when we reached the 1.4 fall factor setup, measuring 8.1 kn. Another way to say this is that we had to reduce the length of the drop by 0.9 meters (or 19%) to make the impact forces comparable. The results Unlike concrete, steel bolts, or springs, there are no exact equations that can absolutely and accurately predict a climbing rope s performance (in terms of impact forces) during a fall. Numerous variables beyond the scope of this article would come into play. However, the 39 drop tests we performed using various combinations of test weights and fall factors have provided much useful information.

4 Heavy climbers beware! Page 4 of 8 1) Fall Factor is key If you haven t acquired a good understanding of fall factor you need to! Perhaps this article and testing results can help provide you with a better understanding. The graph demonstrates one simple rule for all the weights tested, as you increase the fall factor, you reduce your safety because you re generating higher impact forces. The most applicable real-world climbing situation is the possible short fall onto your belayer or first piece(s) of protection during a multi-pitch climb. Be especially wary of these short falls as they might generate higher forces than you d expect. As much as possible, keep the fall factors low by NOT being sparse on your pro when leaving the belay to start that next pitch. Figure 3 2) Greater weight = greater impact force Looking at all the tests from the same drop height (holding the fall factor constant), it is clear that as you increase the test mass the impact force also increases. You can see this in the graph by picking any fall factor and going straight up, noting where each test mass line is intersected. This relationship would also be true for other fall factors and test masses that are not presented here. 3) Dangerous loads It is important to realize that our carabiners, bolt hangers, pieces of pro, etc. are directly related to this 12 kn upper limit for ropes. Without going into all the details, the widely accepted rule of thumb is that the top piece of gear in your system will experience 2/3 MORE force than that felt by the falling climber (see figure 3 for example). So, one could apply this rule using any of these test result impact forces (see data table and graph) and estimate the forces on other pieces of gear in the protection system. Take this test result for example. We found that a 114 kg dropped in a 1.7 fall factor generated 11.1 kn force at the climber s end of the rope. This is dangerously close to the UIAA s 12 kn safety limit! This impact force on the climber s end of the rope translates to 18 kn on the top anchor point. If this number exceeds the capacity of your top anchor pieces they might fail.

5 Heavy climbers beware! Page 5 of 8 By slightly increasing the test mass to 125 kg, it took a lesser fall factor of 1.5 to get about the same 11 kn impact force. Drop that 125 kg in a 1.7 fall factor and we got 12.2 kn = unsafe! Needless to say, the 137 kg test mass reached unsafe territory more quickly. These combinations of weights and fall factors may sound unlikely to ever occur for most climbers. BUT, say you re about a 91 kg climber. How much are you really weighing with all your extra clothes, gear, pack, etc.? Whatever style of climbing you re into, aid, alpine, big-wall, ice, mixed, trad, whatever; it is always critical for you to realize the limitations of all your gear. Remember that heavier loads and higher fall factors ALWAYS add up to higher impact forces that your gear will have to absorb if you fall. Some important notes for all these tests are: 1) The impact forces are measured at the falling climber s end of the rope, NOT the anchor (or belay) end. 2) All impact forces reported here are actual measurements recorded in the PMI laboratory. These test results were not computed with any equations. 3) Each drop was onto an identical but virgin piece of PMI 10.5mm dry treated dynamic rope. As rope is normally used it will lose some of its ability to absorb energy. The impact force values presented here are in a sense actually the best case scenario in terms of the rope s optimal performance. Used ropes would have somewhat higher impact forces. 4) The ropes tested were PMI s 1997 production style and official UIAA test results for these ropes are: 10 falls held, 7.8 kn (1755 lbf) impact force, and an elongation of 6.8%. Other name brands and types of ropes were not tested. IMPORTANT The data presented here should only be used for general comparisons and understanding of the relationship between fall factors, weights, and impact forces. Do not misinterpret the data as an absolute method for determining impact forces. Other name brands, diameters, and types of ropes were not tested and should NOT be assumed to have the exact same numbers. The purpose of this article is simply to share these testing results with the intent of helping climbers make safer climbing situation decisions. The results of this testing may be useful in determining whether a severe fall situation is capable of generating forces high enough to cause failure of a component in a climbing system.

6 Heavy climbers beware! Page 6 of 8 Reference: (1) 1950 s US military parachute research which led to publication of test report WCLE as well as Pilot ejection tests by Henzel in 1967, and Webb in (2) Figures 2 and 3 compliments of BEAL 1999 and Petzl 1996 Catalogs, respectively. Special thanks to: Austin Newman who performed all the testing represented in this article in the PMI drop tower while he worked at PMI for two summers before completing his studies at local UTC. About the author: Chuck Weber has been climbing for 10 years and for the last 5+ years has been putting his engineering background to use as PMI s Quality Manager and ISO System Coordinator. He has the uncommon luxury of access to a UIAA replicate drop tower at PMI. In addition to his routine ISO Quality System and testing duties, he occasionally has the opportunity to do more interesting stuff in the drop tower. This article is one example. This report can also be will soon be available on PMI s website, www/pmirope.com.

7 Heavy climbers beware! Page 7 of 8 Relationship between Impact Forces, Fall Factors, and Masses Impact Force (kn) Fall Factor 137 kg 125 kg 114 kg 102 kg 91 kg 80 kg

8 Heavy climbers beware! Page 8 of 8 Drop Fall Factor drop length (m) Test Weight (lb) Test Mass (kg) Impact force (lbf) Impact force (kn)